Apparatus for minimizing the combustible content of exhaust gases



Oct. 23, 1962 Filed Aug. 13, 1.959

LUMP/P6550? 26 f7 Eff VALl f J. w. SCHNABEL 3,059,419 APPARATUS FOR MINIMIZING THE COMBUSTIBLE CONTENT OF EXHAUST GASES 5 Sheets-Sheet l fiw/Ezwar' JUL /(/5 VV. SCAM/ABEL J. W. SCHNABEL APPARATUS FOR MINIMIZING THE COMBUSTIBLE Oct. 23, 1962 CONTENT OF EmAUsT GASES 3 Sheets-Sheet 2 Filed Aug. 15, 1959 1962 J. w. SCHNA'BEL 3,059,419

APPARATUS FOR IMIZ THE C USTIBLE CONTEN F EXH T GAS Filed Aug. 15, 1959 3 Sheets-Sheet 3 51 r r r 4 98 PW l I 45 32 [EVEN/UP JUL/U5 I4! SCAM/4851.

f7 Q; w 71m; br4- ah ited tats This invention relates to the reduction of combustible materials in exhaust gases from internal combustion engines and the like to make possible the release to the atmosphere of exhaust gases free from irritants, smogproducing ingredients and poisonous compounds. Specifically, the invention deals with the burning of combustibles in exhaust gases from internal combustion engines before releasing the exhaust gases to the atmosphere and while using the heat content of the gases for enhancing the burning operation.

While this invention will hereinafter be specifically described as embodied in an afterburner for the exhaust gases from internal combustion engines, it should be understood that the apparatus of this invention is generally useful for completing the combustion of unburned materials in exhaust or waste gases and therefore the invention in not limited to the preferred herein described specific embodiment.

Internal combustion engines, such as automobile or truck engines, even when efliciently operating, will discharge exhaust gases containing appreciable amounts of carbon monoxide and unburned hydrocarbons. Such engines, even when efficiently operating, will deliver as usable horsepower, only from one-fourth to one-third of the energy of the gasoline or other fuel. The remaining energy is released in the form of heat which is about evenly discharged to the cooling system for the engine and the exhaust gases discharged from the engine. Since unburned materials in automobile exhaust gases are known to contribute greatly in the production of photo chemical smog, many attempts have been made to reduce these unburned ingredients before releasing the exhaust gases to the atmosphere. However, the prior known apparatuses fail to efliciently utilize the heat energy of the exhaust gases to enhance and maintain combustion of the unburned gases. According to this invention, the maximum available heat energy of the exhaust gases is used in the burning of the combustible content of the exhaust gases by mounting an afterburner directly on the engine to receive the hot exhaust gases before these gases lose heat.

The exhaust gas afterburner of this invention preferably takes the form of a manifold mounted directly on the engine to receive exhaust gases directly from each exhaust port of the engine. The manifold has an air inlet for supplying oxygen to the exhaust gases to support combustion of the unburned ingredients in these gases, and the exhaust gas and air mixture is burned in a combustor provided at one end of the manifold. The manifold and combustor are jacketed to provide a surrounding passageway for the burning gases so that the heat energy of these gases can be transferred back to the exhaust gases issuing from the engine for increasing the temperature of the exhaust gases. The burning and burned gases flow in counter-current surrounding relation to the flow of the gases issuing from the engine and are discharged through conventional exhaust pipes and muffler means.

An important feature of this invention is the control of the air supply to the exhaust gases ahead of the combustor as a function of engine speed, intake manifold pressure, and exhaust gas back pressure. This is accomplished by driving an air pump directly from the engine so that its discharge rate is a function of engine speed.

The air discharged from this pump flows through a modu= lating valve sensitive to intake manifold pressure and exhaust gas back pressure to control the proportion of the air from the pump which is to be fed to the exhaust gases. Since intake manifold pressure of the engine is a reliable indication of engine loading and since exhaust gas back pressure determines the minimum pressure necessary for flow of air into the exhaust gases, the control of the modulating valve by the intake manifold pressure and the exhaust gas pressure of the engine results in the automatic supplying of air to the exhaust gases in just enough quantities for supporting complete combustion of the unburned ingredients of the exhaust gases. Thus when loads on the engine are light, the intake manifold vacuum increases and is effective to decrease the air flow to the exhaust manifold. Under these conditions only small amounts of unburned gases will be present in the exhaust gases and a large air supply is not needed and in fact is not Wanted because it might terminate the burning operation in the combustor. Conversely when the engine is operating under heavy load, it is receiving large amounts of fuel, the intake manifold pressure increases and the valve is positioned to admit additional quantities of air to the exhaust gas manifold for supporting combustion of the larger percentage of unburned gases being fed to the combustor.

Since the exhaust gases are burned while their temperature is at a maximum in a manifold which does not impose restrictions on the flow of the gases such as is required in prior known afterburners, the exhaust gas back pressure is considerably lower than was heretofore possible with afterburner equipped engines and more efficient engine operation is obtainable. Further, since the combustor is positioned at the engine, and under the engine hood of the vehicle, the carburetor and intake manifold, also under the hood at the engine, will be heated to operateat high temperatures which aid in the vaporization of the engine intake fuel charge. As a result of higher temperatures for the intake fuel charge, the production of noxious compounds such as aldehydes is greatly reduced and less harmful exhaust gases are fed to the manifold.

It is then an object of this invention to provide an automatically controlled system for minimizing combustibles in engine exhaust gases which utilizes the heat of the exhaust gases to increase the efficiency of the system.

Another object of this invention is to provide an afterburner for burning the combustibles in engine exhaust gases which automatically receives the correct amount of air to support combustion under control of engine speed, exhaust gas pressure, and intake manifold pressure of the engine.

A still further object of this invention is to provide an exhaust gas manifold for internal combustion engines which burns the combustibles in the exhaust gases before releasing the gases to a discharge outlet.

Another and specific object of this invention is to provide an exhaust gas manifold for direct mounting on internal combustion engines to receive exhaust gases directly therefrom and to burn the combustibles in the exhaust gases while adding heat from the burning gases to the exhaust gases just before their combustibles are burned.

A further specific object of this invention is to provide a jacketed exhaust gas manifold for internal combustion engines having an inner passageway receiving gases directly from the exhaust ports of the engine and discharging to a combustor at one end thereof for burning the combustibles in the gases and having a surrounding passageway receiving the burning gases in counterflow relation to the gases in the inner passageway to heat the gases in the inner passageway.

Another object of this invention is to provide an automatic modulating control valve for supplying the correct amount of air to the afterburner of this invention under control of engine intake manifold pressure and exhaust gas pressure.

Still another object of this invention is to provide a system for burning combustibles in engine exhause gases which receives air to support combustion from an engine .driven air compressor.

Other and further objects of this invention will be apparent to those skilled in this art from the following detailed description of the annexed sheets of drawings which, by way of preferred embodiment, only illustrate 'two examples of the invention.

On the drawings:

FIGURE 1 is a front end elevational view of an automobile engine equipped with an afterburner system of this invention.

FIGURE 2 is a top plan view of the engine of FIG- URE '1.

FIGURE .3 is an enlarged transverse cross sectional view of the afterburner exhaust manifold of this invention taken along the line III-III of FIGURE 2 and shown on an enlarged scale.

FIGURE 4 is a longitudinal cross sectional view of the afterburner exhaust manifold taken along the line IVIV of FIGURE 1 and shown on a larger scale.

FIGURE 5 is a view similar to FIGURE 4 but showing a modified afterburner manifold according to this invention.

FIGURE 6 is an enlarged vertical view sectional view of the modulating valve of this invention taken generally along the line VIVI of FIGURE 2..

FIGURE 7 is a fragmentary bottom plan view of the valve of FIGURE 6.

As shown on the drawings:

In FIGURES l and 2 the reference numeral 10 designates generally a conventional V-block internal combustion engine having engine blocks 11, 11 each equipped with an intake manifold 12, 12 receiving an air and fuel charge from a carburetor 13 which in turn receives air from the air filter 14 and fuel from an inlet tube 15. The engine 10 has the conventional engine driven water pump 16 circulating coolant through the jacketed walls of the cylinder blocks 11, 11 and through a radiator 17. A radiator fan '18 mounted on a shaft driven by the engine and projecting from the pump 16 draws air through the radiator '17. A pulley 19 is also provided on this same shaft in front of the pump 16.

In accordance with this invention an afterburner exhaust gas manifold 20, 20 is provided for each engine block 11, 11. Each manifold 20 has flanged inlet nipples 21 mounted directly on the engine block 11 to receive the exhaust gases directly from the exhaust valve ports of the engine. A separate nipple is provided for each exhaust gas port. Each manifold 2t} has a single outlet 22 at the rear end thereof discharging through tubing 23 into a conventional exhaust gas muffler 24 and thence through the conventional tailpipe 25.

Each afterburner exhaust gas manifold 20 also has an air inlet 26 receiving air from an engine driven compressor 27 which is driven through a belt 28 from the pulley 1 9. The compressor discharges through a main tube 29 from which branch tubes 29a, 29a feed the inlets 26. A modulating valve 30 is connected to the air conduit 29 to control air pressure in the branch tubes 29a under the influence of intake manifold pressure and exhaust gas pressure of the engine. As shown in FIGURE 2 the valve 30 has a tube 31 connected to one of the afterburner manifolds 20 and a tube 32 connected to the intake manifold of the engine 10.

As best shown in FIGURES 3 and 4, the afterburner manifold 20 includes an inner casing 33' surrounded by an outer jacket 34 which in turn is covered by a layer of insulation 35. The inner casing 33 has longitudinallyspaced inlet ports 36 along the length thereof each registering with an inlet nipple 21 and directly feeding exhaust gases from the engine into a central elongated chamber 37 provided by the casing. This chamber 37 is closed at its rear end 38 adjacent the rear inlet passage 36 and is open at its front end 39, which is equipped with an outturned flange 40. A combustor 41 is mounted on the front open end 39' of the casing 33 and has a generally cylindrical casing 42 with a large diameter main cylindrical body portion 42a, a converging tapered rear end portion 42b and an outturned flange 43 mounted on the flange 4%. The combustor 41 has an open front end 44 and an apertured flame barrier plate 45 is mounted in the tapered portion 42b of the combustor casing to span the inlet to the main combustor chamber 46 in the cylindrical portion 42a of the casing 42. This plate 45 is composed of a high temperature resisting material and has apertures 45a therethrough which will accommodate free passage of gases from the chamber 37 into the chamber 46 while restricting backward passage of flames from the chamber 46 into the chamber 37.

The air inlet 26 of the manifold 20' is connected through a passageway 47 with the chamber 37 at the front open end 39 of this chamber so as to feed air to the forwardly flowing exhaust gases as they leave the chamber 37. The air and exhaust gases admix upstream of the flame plate 45 in the tapered throat 48 provided by the casing portion 421) of the combustor. The admixed air and exhaust gases are ignited in the chamber 46 of the combustor. A spark plug 49 has the electrodes thereof disposed in the chamber 46 to create a spark that will ignite the gases in the chamber 46 if they are not already ignited by the previous burning gases in the chamber. The spark plug 49 is preferably continuously energized through a suitable electric cable connection 50 to a spark generating means (not shown).

The outer jacket 34 of the manifold provides an annular chamber 51 surrounding the casing 33 and the combustor casing 42. This jacket 34 has a closed front end 52 spaced forwardly from the open front end 44 of the combustor so that gases issuing from the combustor are directed rearwardly through the chamber 5-1 in complete enveloping relationship with the casing 33. The jacket 34 extends beyond the closed end 38 of the casing 33 and converges to the discharge outlet 22 so that the chamber 51 also envelopes the rear end of the casing 33. A helical baffle 54 projects inwardly from the jacket 34 to impart a spiral motion to the gases flowing through the chamber 51 and cause them to efliciently wipe the casing walls 33- for increasing the transfer of heat from the burning and burnt gases in the chamber 51 to the exhaust gases in the chamber 37.

Thus exhaust gases direct from the engine enter the chamber 3-7 through the inlets 36 and flow forwardly to be admixed with air from the passage 47 at the forward discharge end of the chamber 37. The admixed gases and air then pass through the apertures 45a of the flame plate 45 and are ignited in the chamber 46 of the combustor. The burning gases then flow rearwardly around the casing 33 in the passageway 51 and add heat to the gases in the chamber 37. The burned gases substantially freed from any combustible content are then discharged through the conventional muffler system of the vehicle.

In the modification 21M of the afterburner manifold shown in FIGURE 5 parts identical with parts described in FIGURES 3 and 4 have been marked with the same reference numerals. In the modification 20a the air inlet 26a is positioned at the rear end of the manifold instead of at the front end. This inlet 26 discharges into a tube 54 extending centrally through the chamber 37 of the casing 33. The tube has an open discharge end 55 immediately behind the flame plate 45 in the mixing chamber 48 of the combustor 41. In this arrangement therefore, the air passing through the tube 54 is preheated by the exhaust gases in the chamber 37 surrounding the tube and preheated air is then discharged for admixture with these exhaust gases. The afterburner manifold a otherwise operates in the identical manner as the afterburner 20.

The valve 30 for regulating the air flow to the air inlet 26 or 26a, as best shown in FIGURE 6, includes a casing 60 with a depending bottom nipple 61 and an outturned top flange 62. The casing defines a chamber 63 and has a guide boss 64 centrally of the nipple 61 slidably supporting a valve plug 65. This plug has a rounded bottom nose preferably covered with resilient material of good sealing quality such as a rubber cover 66. The bottom of the nipple 61 receives a valve seat ring 67 attached to the nipple as by means of bolts 68 shown in FIGURE 7. The seal: ring 67 has a discharge passageway therethrough and provides a seat for the rubber covered nose 66 of the plug 65.

The nipple 61 defines a chamber 69 around the plug 65 and above the ring 67. This chamber 69 registers with an inlet 70 provided by a boss 71 on a side wall of the nipple 61. This inlet 70 receives the air tube 29 from the compressor 27. Thus since the branch tubes 29a communicate with the air tube 29 in advance of or upstream from the valve chamber 69 in the nipple 61, it follows that the valve 65 is effective to control air pressure in the branch tubes 29a and flow of air through these tubes to the inlets 26 or 26a. When the valve 65 is opened excess air is discharged through the seat ring 67 to the atmosphere.

The plug 65 is controlled by intake manifold pressure and also by exhaust gas pressure by diaphragm actuators pivoted to opposite ends of a link 72 which is pivoted at 73 to the top of the plug.

For mounting the diaphragm actuators, a top casing 74 is provided and is attached to the top flange 62 of the casing 60 by means of mounting screws 75, or the like. This casing 74 has an internal open-ended vertical boss 76 above one end of the lever 72 and a second similar boss 77 above the other end of the lever 72. These bosses slidably support posts 78 and 79 respectively, and the posts project below the bosses to carry transverse pins 80 and 81 which are slidably received in slots 82 and 83 respectively at the outer ends of the link 72.

A flexible diaphragm 84 has a top spanning wall portion 84a centrally secured to the top of the post 78 by a bolt 85 threaded into the top of the post and clamping a part of the spanning wall portion 84a between a cup shaped underlying diaphragm support 86 and a flat top Washer 861:. A coil spring 87 bottomed on the boss 76 urges the cup 86 away from the boss to raise the end of the link 72. The diaphragm has a cylindrical side wall 84b backed by the side wall of the cup 86 and adapted to roll on itself. This side wall terminates in an outturned flange 84c which is clamped around its periphery between the top of the casing 74 and a cover 88 secured to the top of the casing 74. The diaphragm thus seals off a space 89 under the cover from the main chamber 90 of the casing 74.

The space 89 is vented through an inlet 91 in the cover 88 with the tube 31 that leads to the interior of the chamber 37 in one of the manifolds 20 as shown in FIG- URES 2, 4 and 5.

A second and smaller diaphragm 92 has a spanning bottom wall 92a secured to the post 79 by a bolt 93 which clamps the portion 92a between a cup 94 and a fiat washer 94a. The diaphragm has a side wall 92b backed by the side wall of the cup 94 and an outturned flange 92c on the end thereof that is clamped between the top of the casing 74 and a second cover 95 which is secured to the top of the casing 74 by fastening screws 96 or the like. A coil spring 97 bottomed on the cover 95 and on cup 94 urges the post 79 downwardly through the boss 77 until the washer 94a rests on the top of the boss as shown.

The diaphragm 92 is effective to seal off a space 96 under the cover 95 from the main chamber 90 of the casing 74. This space 96 is vented to the tube 32 which leads to the intake manifold 12 as shown in FIGURES 1 and 2 and 6 the cover has an inlet 98 for receiving the end of the tube 32.

The space 89 above the diaphragm 84 is thus vented to exhaust gas pressure in the chamber 37 of the afterburner exhaust manifold, while the space 96 above the diaphragm 92 is vented to intake manifold pressure in the intake manifold 12. An increase in exhaust gas pressure will enlarge the chamber 89 to move the diaphragm 84 downwardly thereby shifting the post 78 downwardly which acts through the lever 72 to seat the plug 65 against the seat 67. Likewise, a decrease in intake manifold vacuum or an increase in intake manifold pressure will enlarge the space 96 to move the diaphragm 92 downwardly thereby shifting the post 79 in a downward direction and also effecting a closing movement of the plug 65. Relative variations in intake manifold pressure and exhaust gas pressure will bring about a tilting of the lever 72 so that the resultant shifting motion on the plug 65 will be influenced by the relative changes in exhaust gas pressure and intake manifold pressure.

Thus, the valve 30 operates in such a manner as to discharge excess air from the main air pipe 29 in accordance with a predetermined difierential relationship between exhaust gas pressure and intake manifold vacuum. When the exhaust gas pressure is high, more intake air pressure to the inlets 26 or 26a is necessary to maintain an intake flow of air to the exhaust gases in the chamber 37. When intake manifold pressure is low, the engine will be operating under reduced loads where the amount of combustibles in the exhaust gases is low and the manifold vacuum will tend to open the valve 65 to dump excess air out of the system. The intake manifold diaphragm is of much smaller effective area than the exhaust gas actuated diaphragm and a relationship of relative areas of the two diaphragms is provided so that the plug 65 will be shifted under varying engine operating conditions to always supply just sufficient air to the manifold passages 37 for supporting combustion of all of the unburned ingredients in the exhaust gases. Since the air compressor is directly driven by the engine and is therefore sensitive to engine speed and since high speed engine operation will result in the development of more exhaust gases than are developed at low speed operation, the compressor is capable of supplying enough air to the exhaust gases at all engine speeds while the modulating valve will automatically take care of excess air not required to support combustion by dumping this excess air through the valve 65 under the joint influence of intake manifold pressure and exhaust gas pressure.

From the above description it will therefore be understood that this invention provides an afterburner exhaust gas manifold for internal combustion engines receiving hot gases directly from the engine, for admix ing these gases with just enough air to support combustion of the unburned constituents in the gases, for burning the gas and air mixture and for utilizing the heat of the burning gases to increase the temperature of the exhaust gases before they are burned to thereby increase the efliciency of the burning operation. The degree of insulation of the cover 35 can be controlled as desired to give up heat to the engine parts under the hood such as for example to heat the fuel charge to the engine. It will be also understood that the supply of air to support combustion of the unburned gases in the exhaust is automatically controlled by the operating conditions of the engine itself under parameters which influence the amount of unburned gases in the exhaust.

It will also be understood that this invention is not limited beyond the scope of the hereinafter appended claims, and that further embodiments and modifications of the invention are included in the scope of the claims.

I claim as my invention:

1. In combination with an internal combustion engine having an engine block, an intake manifold supplying a mixture of fuel and air to said engine block, an engine driven pulley, and an exhaust gas receiving muffler, an

afterburner exhaust gas manifold mounted directly on the engine block to receive exhaust gases directly from the engine before heat is dissipated from said gases, a compressor driven by the engine pulley for supplying air to said exhaust gas manifold, a modulating valve controlling the flow of air from said compressor to said exhaust gas manifold, means controlled by exhaust gas pressure and intake manifold pressure for regulating said valve to control the dumping of excess air from said compressor and thereby regulate the air feed to the exhaust gas manifold, a combustor receiving the mixture of air and exhaust gases from said manifold, a jacket surrounding said manifold receiving burning gases from said combustor, said jacket having an outlet remote from said combustor connected to said muffler, said jacket surrounding said manifold to provide an annular passage for burning gases enroute from the combustor to the discharge outlet for heating the gases and air in the manifold, and electric means in said combustor for maintaining combustion of the unburned combustible materials in the exhaust gases.

2. A system for minimizing the combustible content of exhaust gases from an engine which comprises a casing positioned directly over the engine exhaust ports and receiving exhaust gases directly from the engine exhaust ports, an air compressor driven by the engine, a modulating valve controlled by engine inlet and outlet pressures for regulating air flow from said compressor to said casing, a combustor associated directly with said casing for receiving exhaust gases and air therefrom, means in said combustor for maintaining combustion of the air and exhaust gas mixture, a jacket surrounding said combustor and casing cooperating therewith for defining an annular passageway receiving gases from the combustor to heat the casing and preheat the exhaust gases and air in the casing before they reach the combustor, and a discharge outlet for said jacket remote from said combustor to cooperate with the combustor for flowing burning gases around the casing in countercurrent flow relation to the flow of gases in the casing.

3. A system for minimizing the combustible content of internal combustion engine exhaust gases which comprises an exhaust gas manifold mounted directly on an engine for receiving exhaust gases directly therefrom, a combustor on one end of said manifold for burning gases received therein from the manifold, means in said combustor for maintaining said burning, an apertured flame plate between the combustor and manifold receiving the gases therethrough and preventing backward flow of flames into the manifold, an air compressor driven by the engine for supplying air to said manifold immediately upstream from said flame plate, a modulating valve regulating flow of air from the compressor to said manifold, a first means controlled by exhaust gas pressure in the manifold for shifting said valve, a second means controlled by intake pressure of said engine coacting with said first means to augment the valve closing effect of the first means upon increase in intake pressure of the engine, and means for flowing burning gases from the combustor in heat exchange relation with the manifold to preheat the exhaust gases and air fed to the combustor.

4. A system for reducing the combustible content of internal combustion engine exhaust gases which comprises a casing mounted directly on an engine block, directly over the engine exhaust gas ports and receiving exhaust gases directly from the engine exhaust ports, a combustor mounted on said casing, an air pump driven by the engine supplying air to the exhaust gases intthe casing immediately upstream from the combustor for admixing the air with the exhaust gases fed to the combustor, means for maintaining combustion of the air and exhaust gases in the combustor, means for flowing the burning gases from the combustor in countercurrent heat exchange relation with exhaust gases flowing through the casing, and means for controlling the air fed to the casing under the influence of the pressure of the gases in the casing and the inlet pressure of the engine.

5. An afterburner exhaust gas manifold for an internal combustion engine which comprises an internal casing having a separate inlet port for each exhaust port of an internal combustion engine, a combustor mounted on one end of said casing, a flame plate between the combustor and easing, an air inlet to said casing upstream from said combustor, a jacket surrounding said casing and combustor to define an annular passage therearound in heat exchange relation therewith, said jacket having an outlet remote from said combustor to cooperate for flowing gases through the jacket around the casing in countercurrent flow relation to the flow of gases in the casing, insulation surrounding said jacket to confine the heat of the gases flowing therethrough, and means for supporting combustion in said combustor.

6. An afterburner exhaust gas manifold mounted directly on an engine block for receiving exhaust gases directly from each of the exhaust gas ports of the engine which comprises an elongated insulated jacket having a closed front end and an open rear end, an internal casing in the central portion of said jacket having a closed rear end and an open front end, said internal casing having inlet ports along the length thereof for registering with the exhaust gas ports of the engine, a flame plate spaced inwardly from the front open end of the inner casing separating the easing into an exhaust gas passageway and a combustion chamber downstream from said passageway, an air inlet for supplying air to said exhaust gas passageway upstream from said flame plate, and means for igniting air and exhaust gases discharging through said flame plate and said jacket cooperating with said internal casing to define a passageway for burning gases surrounding the casing to preheat the exhaust gases in the casing.

7. An afterburner exhaust gas manifold for internal combustion engines which comprises an elongated internal casing having a closed rear end, an open front end and inlet ports spaced along the length thereof for directly receiving exhaust gases from an internal combustion engine, a combustor casing on the open front end of said internal casing having an open front end, a jacket surrounding the internal casing and the combustor casing in spaced concentric relation, said jacket having a closed front end spaced forwardly from the open front end of the combustor casing and an open rear end spaced rear- Wardly from the closed end of the internal casing, baffle means in said jacket for directing gases in the jacket into good heat exchange relation with the internal casing, an air inlet discharging into said internal casing adjacent the open end thereof for admixing air with gases flowing from the internal casing to the combustor casing, and means for maintaining combustion of the air and gases in said combustor casing whereby burning gases from the combustor casing will flow through the jacket around the baffie means to the outlet in heat exchange relation with the internal casing for preheating the gases in the internal casing.

References Cited in the tile of this patent UNITED STATES PATENTS 1,260,246 Point Mar. 19, 1918 1,605,484 Thompson et a1 Nov. 2, 1926 1,789,812 Frazer Jan. 20,1931 2,203,554 Uhri et al. June 4, 1940 2,263,318 Tifit Nov. 18, 1941 2,559,623 Holmes July 10, 1951 2,771,736 McKinley Nov. 27, 1956 2,848,186 Bayer Aug. 19, 1958 2,851,852 Cornelius Sept. 16, 1958 

